1. Field of the Invention
The present invention relates to an infrared sensor designed to detect infrared rays with the use of a pyroelectric element and also to a liquid crystal chopper for use in such infrared sensor or the like.
2. Description of Related Art
In an infrared sensor employing a pyroelectric element, a chopper mechanism is required to intermittently cut the infrared rays incident upon the pyroelectric element, so that an output indicative of the detection of infrared rays from the pyroelectric element is continuously obtained. For the chopper mechanism mentioned above, conventionally, a vane-shaped rotary body or vibrating element, etc. has been used. However, this kind of chopper mechanism is disadvantageously bulky in structure and high in cost, with consuming a large amount of electric power.
On the other hand, a liquid crystal shutter has been noted as the chopper mechanism which is stationary and able to be rendered compact in size. For example, Japanese Patent Application Laid-Open No. 62-23412 discloses a liquid crystal chopper of TN (twisted nematic) type. This liquid crystal chopper of TN type is, when it is utilized as a chopper, not free from such a drawback as a long response time (particularly, a fall time). Moreover, the TN-type liquid crystal chopper needs a deflecting plate for infrared rays (wavelength of approximately 3.mu.m-12 .mu.m), which plate is considerably expensive.